1. Field of the Invention
The present invention relates to an inkjet recording head and an inkjet recording apparatus, and more particularly to an inkjet recording head and an inkjet recording apparatus using this head in which the configuration of the electrode leads of a laminated piezoelectric element is designed to ensure higher nozzle density.
2. Description of the Related Art
Conventionally, one known example of an image recording apparatus is an inkjet recording apparatus (inkjet printer) that has an inkjet head (ink discharge head) with an alignment of multiple nozzles, and that forms an image on a recording medium by discharging ink from the nozzles while moving the inkjet recording head and the recording medium relatively to each other.
Various methods for discharging ink in inkjet printers are conventionally known. One known example is a piezoelectric system, wherein changes the volume of a pressure chamber (ink chamber) by deforming a diaphragm that constitute part of the pressure chamber due to the deformation of a piezoelectric body (piezoelectric element) so that controls the ink supply and the ink discharge to the pressure chamber.
The nozzles formed in the inkjet recording head are preferably arranged with higher density in order to improve the performance of such an inkjet recording apparatus and to record high quality images. High-density, two-dimensional arrangement of nozzles is being considered for the purpose of bringing about a page-width head that achieves higher-speed and higher-efficiency recording. In an inkjet recording apparatus in which piezoelectric elements are used, there are known apparatuses that use a laminated piezoelectric body in order to obtain high ink ejection force and excellent controllability.
In an inkjet recording head in which a piezoelectric element is used, the wiring of the lead electrode had to be redesigned in order to increase the efficiency of the production of such an inkjet recording head.
An example of a known wiring structure of a piezoelectric body that dispenses with connecting leads to the piezoelectric transducer to increase productivity comprises a first electrode on the surface facing the pressure chamber of the pressurizing actuator (piezoelectric element); a second electrode in which a portion thereof is provided to the same surface via a gap between the first electrode and which extends to the other surface of the pressurizing actuator; and a third electrode on the surface facing the pressurizing actuator of the pressure chamber, wherein wiring is brought out from one side (specifically, the surface on the pressure chamber side) of a single-layered piezoelectric element (refer to Japanese Patent Application Publication No. 57-167272, and other publications).
Also known is an inkjet recording head designed to eject ink droplets with high efficiency, in which electrode-formation material and piezoelectric material are alternately laminated, and in which a pressurizing actuator is configured so that an active area is formed in the center portion, and expansion and contraction occur in the direction of lamination, wherein the pressurizing actuator and a fixed plate form a contact area solely in the active area, and by fixing both components exclusively in the contact area, the active area alone expands in the direction of lamination when a drive signal is applied, the stress of the edge portion of the pressurizing actuator is low, and the degree of expansion in the direction of the electrode arrangement is made larger (refer to Japanese Patent Application Publication No. 6-226971, and other publications).
Also known is a structure in which an inactive portion of the piezoelectric body that is essentially not driven is provided to the external side of the active portion of the piezoelectric body, the effect of the electric field in the edge of the inactive portion of the piezoelectric body produced by the application of voltage to the active portion of the piezoelectric body is eliminated by a configuration in which the distance from the edge of the inactive portion of the piezoelectric body to the edge of the active portion of the piezoelectric body is substantially triple or more the thickness of the piezoelectric layer, and the inactive portion of the piezoelectric body is not driven. Although the piezoelectric layer is not laminated, the piezoelectric body and the electrode are formed into a stepped structure that prevents peeling and cracking in the edges of the active portion of the piezoelectric body (refer to Japanese Patent Application Publication No. 11-105281, and other publications).
Also known is a droplet ejection apparatus in which voltage is applied to the plates of piezoelectric material by using a first electrode and second electrode disposed inside the piezoelectric material in a configuration in which the piezoelectric material in the form of sheets is laminated, and droplets are ejected, wherein the piezoelectric material is formed across the entire surface of the liquid chamber, but the electrode pattern of the first electrode is formed so that the surface area thereof becomes sequentially smaller from the lower portion to the upper portion in the thickness direction of the plates of piezoelectric material, the electrode pattern of the second electrode is formed so that the surface area thereof becomes sequentially larger from the lower portion to the upper portion in the thickness direction of the plates of piezoelectric material, the plates of piezoelectric material are deformed in the expansion and contraction direction that is sloped in the direction of the surface thereof by applying voltage from the first and second electrodes to eject droplets, thereby improving the energy efficiency and imparting an adequate amount of deformation to the plates of piezoelectric material even if the drive voltage is low (refer to Japanese Patent Application Publication No. 2002-292865, and other publications).
Another known art is one in which a nozzle plate, an ink flow channel plate, an insulating plate, a bimorphous polyvinylidene fluoride (PVDF) plate, and a flexible print substrate are sequentially laminated and an inkjet head is adhesively formed, wherein through holes for electrical connections are formed in the bimorphous PVDF plate and the flexible print substrate, and the head electrically connected from one side (refer to Japanese Patent Application Publication No. 61-79669, and other publications, and particularly FIG. 1 of Japanese Patent Application Publication No. 61-79669).
Also known is an apparatus in which a common electrode is formed and on both sides of a laminated piezoelectric member composed of two layers, individual electrodes are disposed in the boundary portion of the two layers, and the electrode layers are formed into steps (refer to Japanese Patent Application Publication No. 10-264389, and other publications, and particularly FIG. 6 of Japanese Patent Application Publication No. 10-264389).
However, there are drawbacks when a laminated piezoelectric body is used to achieve a higher nozzle density in the inkjet recording heads described above in that the head cannot be wired from the side, and it is difficult to achieve high-density integration. More particularly, it is difficult to dispose the laminated piezoelectric bodies in a high-density, two-dimensional arrangement because, in the laminated piezoelectric element of prior art cited in Japanese Patent Application Publication No. 6-226971, for example, piezoelectric material and electrode formation material are alternately laminated, the resulting laminate with large dimensions is baked, and the laminate is then cut with a diamond saw or the like to manufacture a head.
Because such a laminate is cut into strips to manufacture a head, only rectangular laminated piezoelectric bodies can be fabricated, and the piezoelectric layers that form the laminate must have the same shape. Therefore, the surface area of the active portion of the piezoelectric body is made as large as possible, and there is a limit to increasing force from the piezoelectric body.
This is due to the fact that wiring is conventionally performed after the piezoelectric body is mounted in the inkjet recording head, and a gap is therefore required to prevent the wiring of adjacent piezoelectric elements from shorting, and work to provide side surface wiring is required.
Also, the apparatus cited in Japanese Patent Application Publication No. 2002-292865 is formed so that the size of the electrodes disposed inside the plates of piezoelectric material sequentially become smaller, and because the size of the plates of piezoelectric material covers the entire surface of the liquid chamber, the wiring from one surface of the piezoelectric body does not have a structure that allows a connection, and there is still a drawback in that it is difficult to achieve higher density.
The piezoelectric bodies cited in Japanese Patent Application Publication Nos. 57-167272 and 11-105281 are single-layered and not laminated piezoelectric bodies, the structure is completely different from inkjet recording heads that use laminated piezoelectric elements, and there is a drawback in that it is difficult to apply these bodies to art aimed at increasing density using laminated piezoelectric elements.
The art cited in Japanese Patent Application Publication No. 61-79669 provides through holes to make electrical connections to a bimorphous PVDF plate and a flexible print substrate, and there the drawback is that it is difficult to achieve a higher density. Also, a configuration suitable for a method of connecting laminated piezoelectric bodies composed of a greater number of layers is not disclosed in Japanese Patent Application Publication No. 61-79669.
In the apparatus cited in Japanese Patent Application Publication No. 10-264389, the common electrode and individual electrodes are disposed adjacent to each other, and the drawback is that it is still difficult to achieve a higher density. Furthermore, a configuration suitable for a method of connecting laminated piezoelectric bodies composed of a greater number of layers is not disclosed in Japanese Patent Application Publication No. 10-264389, either.